1. Field of the Invention
This invention relates to a process for preparing substituted formamides by the catalytic oxidation of substituted tertiary amines. It is more particularly directed to such a process in which the catalyst is a metal halide used in conjunction with an adjunct which is an alkali metal halide or ammonium halide.
2. Description of the Prior Art and Summary of the Invention
It is well known that substituted formamides can be prepared from tertiary amines by catalytic oxidation. One such method is shown in U.S. Pat. No. 3,483,210 to Rosenblatt and Davis.
Another catalytic oxidation method is shown in U.S. Pat. No. 4,042,621 to Sauer. In that method, a tertiary amine is catalytically oxidized to a corresponding formamide using as the catalyst a soluble chloride, bromide or iodide of cobalt, copper, gold, iron, manganese, mercury, nickel, palladium, platinum, rhenium, silver or zinc.
The Sauer process is an excellent one and gives good conversion of trimethylamine to the commercially desirable dimethylformamide, particularly when copper halides, especially CuCl.sub.2, are used as catalysts. As is well known, however, copper halides are quite corrosive to metals such as stainless steel ordinarily used in fabricating chemical processing equipment, and use of the Sauer process in a practical commercial way therefore requires that equipment be made of titanium. Moreover, in the reaction, the copper halides are oxidized to oxyhalides, which are noncatalytic and which are insoluble in the reaction mass and precipitate out. These oxyhalides are difficult to redissolve and so must be removed, which interferes with the continuity of the reaction.
It has now been found, according to the invention, that the corrosion is minimized and that solubility of the catalyst in the reaction medium is generally increased if the catalyst is used in conjunction with an adjunct which is a chloride, bromide or iodide of sodium, potassium, lithium or ammonium. Use of the combination also significantly improves the selectivity of the oxidative conversion of trimethylamine to dimethylformamide.